“Switchable glass” is an industry term for glass that can be switched back and forth between an opaque or translucent state to a clear transmissive or transparent state by the application of electricity. This product is also commonly referred to as electric privacy glass.
The glass industry has long desired a useful, inexpensive, and easy to produce version of electric privacy glass. However, the industry has not yet been able to provide a product that is feasible to produce or that has the strength and longevity characteristics demanded by customers and regulatory boards. For example, existing products tend to be expensive, such as in the range of from $100 to $200 per sq. ft. and typically carry a maximum warranty of 1 year. As a result, currently available products tend to be relegated to a small niche of specialty architectural projects.
Existing electric privacy glass products are typically made using the same general process and materials. To begin with, a thin film of metallic coating is sputter coated on a sheet of Mylar film. A liquid crystal and epoxy mixture is then roller coated on to the coated Mylar film. The composite film is then glued between two pieces of glass using urethane glue.
Several problems exist with this method and product. First, it is expensive to sputter a metallic coating on Mylar. Second, the metallic coating on the Mylar film is amorphous, meaning it does not want to stick to the Mylar film. This means that when the glass pieces are glued together with the Mylar film placed therebetween, a very weak bond is formed because the liquid crystal-epoxy mixture and the urethane glue holding the glass together are bonded to the metallic coating which does not have a strong bond to the Mylar film. Also, there is an inherent problem with using a mixture of liquid crystal and epoxy, Mylar film, and glass together due to their different rates of expansion under environmental conditions. When exposed to changes in heat, humidity, and UV light, the different materials expand and contract at different rates, resulting in the product delaminating, which results in a product having a relatively short life span. This is part of the reason why current products cannot be given extended product warranties.